1. Field of the Invention
The present invention relates generally to electrical wiring devices, and particularly to power control wiring devices.
2. Technical Background
Power control devices allow a user to adjust the amount of current delivered to an electrical load, such as a light or a motor. When the electric load is a lighting device, the power control device is commonly referred to as a dimmer. If the power control device is configured to control a motor, such as a fan motor, the power control device is referred to as a motor speed controller. Motor speed controllers are also used to control the speed of machinery such as power tools, electric drills, chair lifts, stationary machinery, and other such variable speed motor driven elements.
The core component of the power control device is commonly referred to as a series pass element. The amount of current provided by the series pass element is varied by a user-actuated switch mechanism. The switch mechanism may be a continuously variable switch or a selector switch mechanism that selects from a predetermined number of discrete switch settings. The series pass element may be implemented using a solid state switch. The active switching element in a solid state switch may be a transistor, a MOSFET device, a gate turn-off device, or a thyristor device, such as silicon controlled rectifier (SCRs) or a triac device. When the series pass element in a fan speed control device is a variable impedance, the power control device is commonly referred to as a “dehummer.”
As those of ordinary skill in the art will appreciate, power control devices are typically packaged in a wiring device form factor for installation in an outlet box. Of course, one or more of the power control devices described above may be disposed within the device housing. A unit equipped with both a fan motor and a lighting element, for example, may be controlled by a wiring device that includes both a dimmer and a fan speed control. The exterior of the wiring device includes either screw terminals or wire terminals for subsequent connection between the AC power source and the load. The wiring device form factor also provides a user accessible front face that is includes one or more switch mechanisms such as levers, dials, slide switches, and other such input control mechanisms that permit a user to vary the power to a load.
Prior to device installation, wiring from the AC power source and wiring to the load(s) are disposed inside the outlet box. The outlet box is usually located proximate to the load being controlled. The device is installed by connecting the wiring inside the outlet box to the appropriate wiring device terminals disposed on the exterior of the wiring device. The power control wiring device is then inserted into the outlet box and attached to the outlet box using one or more fasteners. A cover plate is installed to complete the installation.
Some of the drawbacks associated with conventional power control devices are illustrated by referring to FIG. 1. Conventional device 10 includes a dimmer control knob 12 and switch 14 disposed in a protective frame 16. The protective frame 16 is coupled to mounting strap 20. The frame 16 functions as an alignment mechanism for the cover plate (not shown). The frame 16 extends through the cover plate opening when the device installation is complete. The mounting strap 20 is hidden behind the cover plate.
One drawback to this approach relates to the additional costs and complexity associated with the frame itself. Frame 16 represents an additional part that must be molded or stamped during the fabrication process. Further tooling and/or labor is required to assemble the frame 16, dimmer control 12, and switch 14 to mounting strap 20. Thus, the elimination of a superfluous framing element translates to a device that is easier and cheaper to manufacture. Protective frame 16 also requires a specially sized, non-standard wall plate. This option is less attractive to users because of the difficulty in acquiring a replacement cover plate in the event that it becomes cracked or damaged. Wall plates conforming to the dimensional characteristics defined by the ANSI/NEMA WD6 standard are ubiquitous and easily obtained in an after market transaction.
Another drawback to conventional devices relates to device cleaning and maintenance issues. The protective frame 16 creates dust collecting crevices between the frame and the switch elements, and between the frame and the wall plate. Recessed surface 24 also tends to collect dirt and grime. On the other hand, the crevices and recessed surfaces are difficult to reach and, therefore, difficult to keep clean. Accordingly, unsightly dirt and grime tend to accumulate in the crevices and on the recessed surface 24. To make matters worse, dust particles have a tendency to migrate into the interior of device 10. Those of ordinary skill in the art will appreciate that dust build-up may effect the operation of interior switch components.
Yet another drawback to the conventional device shown in FIG. 1 relates to the lack of a locator lamp or pilot light. A person unfamiliar to the layout of the living space may have difficulty locating the power control wiring device when the space is darkened. The person attempts to “feel” his way around the room in an attempt to locate the dimmer switch. Obviously, this scenario represents a safety hazard. One approach that may be considered incorporates a dedicated lamp into the device housing. Of course, this approach has its own drawbacks. Dedicated lamps of this nature are permanently illuminated. When the lamp burns out, the entire wiring device must be replaced as well.
What is needed is a power control device that includes self aligning user-actuated switching elements that eliminate superfluous framing elements and is easier and relatively less costly to produce. What is also needed is a power control device that employs wall plates that conform to the ANSI/NEMA WD6 standard for wall plates. What is further needed is a power control device that eliminates the cleaning and maintenance issues of conventional devices. Finally, a power control device is needed that includes a modular light assembly that includes a removable light module.